Systems and methods for output current regulation in power conversion systems

ABSTRACT

Systems and methods are provided for regulating a power conversion system. An example system controller includes: a detection component configured to receive an input voltage related to a diode connected to an inductor and output a first signal at a first logic level in response to the input voltage being larger than a predetermined threshold, a control logic component configured to receive the first signal, process information associated with the first signal, and output a modulation signal related to a modulation frequency in response to the first signal being at the first logic level, and a driving component configured to receive the modulation signal and output a drive signal to open and close a first switch at the modulation frequency.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201410166772.2, filed Apr. 23, 2014, incorporated by reference hereinfor all purposes.

2. BACKGROUND OF THE INVENTION

Certain embodiments of the present invention are directed to integratedcircuits. More particularly, some embodiments of the invention provide asystem and method for output current regulation. Merely by way ofexample, some embodiments of the invention have been applied to powerconversion systems. But it would be recognized that the invention has amuch broader range of applicability.

FIG. 1 is a simplified diagram for a conventional buck power conversionsystem with primary-side sensing and regulation. The system 100 includesa system controller 102, resistors 118, 164, and 192, capacitors 108,142, and 124, a power switch 130, an inductor 120, a diode 122, and LEDs198. In addition, the system controller 102 includes terminals 140, 144,146, 148 and 134.

An alternating-current (AC) input 110 (e.g., VAC) is provided to inputterminals 112 and 114. For example, the system controller 102 receivesan input signal related to the AC input 110 and generates a signal 194to affect the switch 130. When the switch 130 is closed (e.g. beingturned on), the inductor 120 is magnetized and a current 190 flowsthrough the switch 130 and the resistor 164. A current sensing signal106 is detected by the system controller 102 at the terminal 146 (e.g.,terminal CS). When the switch 130 is open (e.g., being turned off), theinductor 120 is demagnetized, and a current 192 flows through the diode122, the capacitor 124, and the LEDs 198. The output current 188 thatflows through the LEDs 198 is approximately equal to an average currentflowing through the inductor 120. If the average current flowing throughthe inductor 120 is regulated to a predetermined magnitude, the outputcurrent 188 that flows through the LEDs 198 is regulated to beapproximately constant at a predetermined magnitude. For example, theoutput current 188 is estimated by sensing the current 190 through theresistor 164 and calculating a demagnetization period associated withthe inductor 120. The terminal 148 is biased at a ground voltage 104.But the conventional power conversion system 100 has some disadvantages.

Hence, it is highly desirable to improve the technique for regulatingoutput currents of power conversion systems.

3. BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the present invention are directed to integratedcircuits. More particularly, some embodiments of the invention provide asystem and method for output current regulation. Merely by way ofexample, some embodiments of the invention have been applied to powerconversion systems. But it would be recognized that the invention has amuch broader range of applicability.

According to one embodiment, a system controller for regulating a powerconversion system includes: a detection component configured to receivean input voltage related to a diode connected to an inductor and outputa first signal at a first logic level in response to the input voltagebeing larger than a predetermined threshold; a control logic componentconfigured to receive the first signal, process information associatedwith the first signal, and output a modulation signal related to amodulation frequency in response to the first signal being at the firstlogic level; and a driving component configured to receive themodulation signal and output a drive signal to open and close a firstswitch at the modulation frequency, so that in response to the firstswitch being closed, the inductor is configured to output a firstcurrent through the switch and in response to the first switch beingopen, the inductor is configured to output a second current through thediode.

According to another embodiment, a system controller for regulating apower conversion system includes: a first transistor including a firsttransistor terminal, a second transistor terminal, and a thirdtransistor terminal, the first transistor terminal being coupled to afourth transistor terminal of a second transistor, the second transistorfurther including a fifth transistor terminal and a sixth transistorterminal. The fifth transistor terminal is coupled to a first resistorterminal of a first resistor, the first resistor further including asecond resistor terminal. The fifth transistor terminal is coupled to afirst diode terminal of a first diode, the first diode further includinga second diode terminal. The second diode terminal is coupled to thesecond resistor terminal. The system controller is configured to changea first voltage of the fourth transistor terminal to turn on and off thesecond transistor and to affect a current flowing through an inductor.

According to yet another embodiment, a system controller for regulatinga power conversion system includes: a sampling component configured todetect one or more peak magnitudes of a current sensing signalassociated with a first current from an inductor flowing through aswitch and generate an output signal based on at least informationassociated with the detected one or more peak magnitudes of the currentsensing signal; an error amplifier configured to receive the outputsignal and a reference signal and generate an amplified signal based onat least information associated with the output signal and the referencesignal; a comparator configured to receive the current sensing signaland a first signal associated with the amplified signal and output acomparison signal based on at least information associated with thefirst signal and the current sensing signal; and a control-and-drivecomponent configured to receive the comparison signal and output a drivesignal based on at least information associated with the comparisonsignal to close or open the switch to affect the first current.

According to yet another embodiment, a system controller for regulatinga power conversion system includes: a protection component configured toreceive a first signal and a second signal and generate a third signalbased on at least information associated with the first signal and thesecond signal, the first signal being associated with a demagnetizationperiod related to a inductor, the second signal being associated with afirst current flowing through the inductor; and a control-and-drivecomponent configured to receive the third signal and output a drivesignal to the switch to affect the first current. The protectioncomponent is further configured to, in response to, the second signalindicating, during a first switching cycle associated with the drivesignal, that the first current is equal to or larger then a currentthreshold, and the first signal indicating, during an off-time period ofthe first switching cycle, that the demagnetization period is smallerthan a predetermined time period, change the third signal from a firstsignal state to a second signal state to cause the power conversionsystem to be shut down.

In one embodiment, a method for regulating a power conversion systemincludes: receiving an input voltage related to a diode connected to aninductor, processing information associated with the input signal;outputting a first signal at a first logic level in response to theinput voltage being larger than a predetermined threshold; receiving thefirst signal; and processing information associated with the firstsignal. The method further includes: outputting a modulation signalrelated to a modulation frequency in response to the first signal beingat the first logic level; receiving the modulation signal; andprocessing information associated with the modulation signal. Inaddition, the method includes: outputting a drive signal to open andclose a first switch at the modulation frequency; in response to thefirst switch being closed, outputting a first current through theswitch; and in response to the first switch being open, outputting asecond current through the diode.

In another embodiment, a method for regulating a power conversion systemincludes: sampling one or more peak magnitudes of a current sensingsignal associated with a first current from an inductor flowing througha switch; generating an output signal based on at least informationassociated with the detected one or more peak magnitudes of the currentsensing signal; receiving the output signal and a reference signal; andprocessing information associated with the output signal and thereference signal. The method further includes: generating an amplifiedsignal based on at least information associated with the output signaland the reference signal; receiving the current sensing signal and afirst signal associated with the amplified signal; processinginformation associated with the current sensing signal and the firstsignal; and outputting a comparison signal based on at least informationassociated with the first signal and the current sensing signal.Furthermore, the method includes: receiving the comparison signal;processing information associated with the comparison signal; andoutputting a drive signal based on at least information associated withthe comparison signal to close or open the switch to affect the firstcurrent.

In yet another embodiment, a method for regulating a power conversionsystem includes: receiving a first signal and a second signal;processing information associated with the first signal and the secondsignal; and generating a third signal based on at least informationassociated with the first signal and the second signal, the first signalbeing associated with a demagnetization period related to an inductor,the second signal being associated with a first current flowing throughthe inductor. The method further includes: receiving the third signal;processing information associated with the third signal; outputting adrive signal to the switch to affect the first current; and in responseto, the second signal indicating, during a first switching cycleassociated with the drive signal, that the first current is equal to orlarger than a current threshold and the first signal indicating, duringan off-time period of the first switching cycle, that thedemagnetization period is smaller than a predetermined time period,changing the third signal from a first signal state to a second signalstate to cause the power conversion system to be shut down.

Depending upon embodiment, one or more of these benefits may beachieved. These benefits and various additional objects, features andadvantages of the present invention can be fully appreciated withreference to the detailed description and accompanying drawings thatfollow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram for a conventional floating buck powerconversion system with primary-side sensing and regulation.

FIG. 2 is a simplified diagram showing a power conversion systemaccording to a embodiment of the present invention.

FIG. 3 is a simplified timing diagram for the power conversion system asshown in FIG. 2 according to an embodiment of the present invention.

FIG. 4 is a simplified diagram showing a power conversion systemaccording to another embodiment of the present invention.

FIG. 5 is a simplified diagram showing a power conversion systemaccording to yet another embodiment of the present invention.

FIG. 6 is a simplified diagram showing a power conversion systemaccording to yet another embodiment of the present invention.

FIG. 7 is a simplified diagram showing a power conversion systemaccording to yet another embodiment of the present invention.

FIG. 8 is a simplified timing diagram for demagnetization detection ofthe power conversion system a shown in FIG. 2 , the power conversionsystem a shown in FIG. 4 , the power conversion system as shown in FIG.6 and/or the power conversion system as shown in FIG. 7 according tosome embodiments of the present invention.

FIG. 9 is a simplified diagram showing certain components of ademagnetization detector as part of the power conversion system as shownin FIG. 2 , certain components of a demagnetization detector as part ofthe power conversion system as shown in FIG. 4 , certain components of ademagnetization detector as part of the power conversion system as shownin FIG. 6 , and/or certain components of a demagnetization detector aspart of the power conversion system as shown in FIG. 7 according to someembodiments of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the present invention are directed to integratedcircuits. More particularly, some embodiments of the invention provide asystem and method for output current regulation. Merely by way ofexample, some embodiments of the invention have been applied to powerconversion systems. But it would be recognized that the invention has amuch broader range of applicability.

FIG. 2 is a simplified diagram showing a power conversion systemaccording to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The system 200 includes a system controller 202, resistors 208, 209.218,236 and 267, a full-wave rectifying bridge 213, capacitors 224, 234 and242, a switch 230, an inductor 220, diodes 222 and 238, and LEDs 298.The system controller 202 includes a switch 232, a diode 250, a voltageclamper 252, a reference signal generator 258, ma input-voltage detector260, ma enable controller 262, a demagnetization detector 264, a valleydetector 266, a control logic component 268, a comparator 270, a drivingcomponent 272, a summation component 274, ahigh-low-input-line-voltage-compensation component 276, and a leadingedge blanking (LEB) component 278. In addition, the system controller202 includes terminals 231, 240, 246, 248 and 254. For example, theswitch 230 includes a transistor (e.g., a field effect transistor, aninsulated-gate bipolar transistor, or a bipolar junction transistor). Inanother example, the switch 232 includes a transistor (e.g., a fieldeffect transistor, an insulated-gate bipolar transistor or a bipolarjunction transistor). In another example, the terminal 248 (e.g.,terminal GND) is biased at a ground voltage 204 (e.g., chip ground). Inyet another example, the resistor 236 and the diode 238 we configured toadjust a turn-on/turn-off speed of the switch 230. As a example, avoltage associated with a gate terminal of the switch 230 is notconstant during a transient period when the switch 230 is turned on orturned off. As another example, the voltage associated with the gateterminal of the switch 230 is constant during a time period long beforeor after the switch 230 is turned on or turned off.

According to one embodiment, an AC input 210 (e.g., VAC) is provided toinput terminals 212 and 214, and the rectifying bridge 213 isconfigured, together with the capacitor 242, to provide a rectifiedinput voltage 201 (e.g., V_(bus)). For example, the input voltage 201(e.g., V_(bus)) is processed by a voltage divider including theresistors 208 and 209, and the system controller 202 receives an inputsignal 219 at the terminal 254 (e.g., terminal V_(bus)). In anotherexample, the input-voltage detector 260 receives the input signal 219and outputs a signal 280 to the enable controller 262 that generates asignal 281 to the control logic component 268. In yet another example,the control logic component 268 outputs a modulation signal 282 to thedriving component 272 that generates a drive signal 283 to affect (e.g.,control) the switch 232.

According to another embodiment, the switch 232 and the switch 230 areconnected in cascode. For example, the switch 232 is closed or openedfor power switching. In another example, during an on-time period of aswitching cycle associated with the drive signal 283, the switch 232 isclosed (e.g., being turned on). In yet another example, a voltage signal284 associated with a node (e.g., node SW) between the switches 230 and232 decreases in magnitude, and in response the switch 230 is closed(e.g., being turned on). In yet another example, the inductor 220 ismagnetized, and a current 290 flows through the switch 230 and isreceived by the system controller 202 at the terminal 231. In yetanother example, a voltage 237 associated with a node between the switch230 and the inductor 220 decreases in magnitude. In yet another example,a voltage signal 206 associated with the resistor 267 is detected by thesystem controller 202 at the terminal 246 (e.g., terminal CS), and theLEB component 278 receives the signal 206 and outputs a current sensingsignal 277 to the comparator 270. In yet another example, during anoff-time period of a switching cycle associated with the drive signal283, the switch 232 is open (e.g., being turned off). In yet anotherexample, the signal 284 increases in magnitude, and in response theswitch 230 is opened (e.g., being turned off). In yet another example,the inductor 220 is demagnetized, and a current 292 flows through thediode 222, the capacitor 224, and the LEDs 298. In yet another example,the signal 237 increases in magnitude (e.g., to become close to thevoltage 201). In yet another example, an output current 288 that flowsthrough the LEDs 298 is associated with (e.g., equal to) ma averagecurrent flowing through the inductor 220. In yet another example, if theaverage current flowing through the inductor 220 is regulated to apredetermined magnitude, the output current 288 that flows through theLEDs 298 is regulated to be approximately constant at a predeterminedmagnitude.

According to yet another embodiment, the signal 284 associated with thenode SW between the switches 230 and 232 is received by thedemagnetization detector 264 that is configured to determine ademagnetization period associated with the inductor 220. For example,the valley detector 266 receives a detection signal 285 from thedemagnetization detector 264 and outputs a signal 286 to the controllogic component 268. As an example, the valley detector 266 detects afirst valley appearing in de signal 284 and changes the signal 286 so taa rising edge appears in the drive signal 283 end an on-time period of aswitching cycle associated with the drive signal 283 begins. Forexample, the output current 288 is estimated based on at leastinformation associated with the signal 206 and the demagnetizationperiod associated with the inductor 220.

In one embodiment, during a start-up process of de system 200, thecapacitor 234 is charged in response to the voltage signal 201 (e.g.,through the resistor 218), and a voltage 235 increases in magnitude. Forexample, if the voltage signal 235 becomes larger than a start-upthreshold voltage, the controller 202 begins to operate. As an example,the signal 219 related to (e.g., proportional to) the voltage signal 201is sensed by the input-voltage detector 260. In another example, if thevoltage signal 201 is smaller than a predetermined threshold, theinput-voltage detector 260 outputs the signal 280 at a first logic level(e.g., 0), and if the voltage signal 201 is larger than thepredetermined threshold, the input-voltage detector 260 outputs thesignal 280 at a second logic level (e.g., 1). In yet another example, ifthe input-voltage detector 260 changes the signal 280 from the firstlogic level (e.g., 0) to the second logic level (e.g., 1), the enablecontroller 262 changes the signal 281 (e.g., to a logic high level). Inyet another example, the control logic component 268 outputs themodulation signal 282 to turn on and off the switch 232 at a modulationfrequency, so that the system 200 operates normally and the LEDs 298 areturned on. Thereafter, the enable controller 262 does not change thesignal 281 in response to the signal 280. In some embodiments, thevoltage signal 201 is always sensed by the input-voltage detector 260during the operation of the system 200. In other embodiments, thevoltage signal 201 is sensed by the input-voltage detector 260 duringthe start-up process and/or a short time period thereafter.

In another embodiment, when the switch 232 is opened (e.g., being turnedoff), the voltage 237 begins to increase in magnitude immediately afterthe switch 232 is opened. For example, the switch 230, the inductor 220and the associated parasitic capacitances begin to oscillate. In anotherexample, one or more spikes begin to appear in the signal 284 associatedwith the node (e.g., node SW) between the switch 230 and the switch 232.In yet another example, if the one or more spikes are larger than aclamping voltage associated with the voltage clamper 252 (e.g., a zenerdiode) plus a forward voltage associated with the diode 250, the spikesare absorbed by the capacitor 234 and the voltage clamper 252 throughthe diode 250. In yet another example, the one or more spikes providesupply charges or currents to the capacitor 234 to provide a supplyvoltage to the controller 202 through the terminal 240 (e.g., terminalVCC) for all internal circuits of the controller 202. In yet anotherexample, the summation component 274 receives a compensation signal 271from the high-low-input-line-voltage-compensation component 276 and areference signal 273 and outputs a threshold signal 275 to thecomparator 270 that outputs a comparison signal 299. In yet anotherexample, if the comparison signal 299 changes from a first logic level(e.g., 1) to a second logic level (e.g., 0) which indicates that thecurrent sensing signal 277 becomes larger than the threshold signal 275in magnitude, a falling edge appears in the drive signal 283 and anon-time period of a switching cycle associated with the drive signal 283ends. In yet another example, if the input line voltage (e.g., thesignal 201) has a large magnitude, the signal 271 has a small magnitude(e.g., 0). In yet another example, if the input line voltage (e.g., thesignal 201) has a small magnitude, the signal 271 has a large magnitude.As an example, the voltage signal 201 is inversely proportional to thesignal 271 in magnitude.

FIG. 3 is a simplified timing diagram for the power conversion system200 as shown in FIG. 2 according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. For example,the waveforms 302, 304 and 306 describe certain operation of the powerconversion system 200 that operates in a discontinuous conduction mode(DCM). The waveform 302 represents the signal 284 associated with thenode SW as a function of time, the waveform 304 represents the current292 flowing through the inductor 220 as a function of time, and thewaveform 306 represents the current sensing signal 277 as a function oftime. In some embodiments, the waveform 302 represents the voltage 237associated with the node between the switch 230 and the inductor 220 asa function of time.

According to one embodiment, during an on-time period of the switch 232(e.g., between t₀ and t₁), the signal 284 has a low magnitude 318 (e.g.,zero), as shown by the waveform 302. For example, the current 292increases from a magnitude 310 to a peak magnitude 312 (e.g., as shownby the waveform 304), and the current sensing signal 277 increases froma magnitude 314 to a magnitude 316 (e.g., as shown by the waveform 306).In another example, at t₁, the switch 232 is opened (e.g., being turnedoft), and the inductor 220 begins to demagnetize. In yet anotherexample, the signal 284 increases from the magnitude 318 to a magnitude320 and keeps at the magnitude 320 until the end of a demagnetizationperiod of the inductor 220 (e.g., A at t₂), as shown by the waveform302. In yet another example, during the demagnetization period, thecurrent 292 decreases from the peak magnitude 312 (e.g., at t₁) to amagnitude 322 (e.g., at t₂ as shown by the waveform 304). In yet anotherexample, at t₁, the current sensing signal 277 decreases from themagnitude 316 to a magnitude 324 and keeps at the magnitude 324 duringthe demagnetization period (e.g., as shown by the waveform 306). In yetanother example, after the demagnetization period, the signal 284decreases from the magnitude 320 (e.g., at t₂) to a magnitude 326 (e.g.,B at t₃) which corresponds to a first valley appearing in the signal284.

According to another embodiment, an average current 308 flowing throughthe inductor 220 is determined as follows:

IL_avg=½×IL_P  (1)

where IL_avg represents the average current 308, and IL_P represents thepeak magnitude 312 of the current 292. As an example, the peak magnitude312 is determines as follows:

$\begin{matrix}{{IL\_ P} = \frac{V\_ th}{R_{S}}} & (2)\end{matrix}$

where V_th represents the threshold signal 275, and R_(S) represents theresistor 267. Combining Equation 1 and Equation 2, the average current306 flowing through the inductor 220 is determined as follows:

$\begin{matrix}{{IL\_ avg} \approx {\frac{1}{2} \times \frac{V\_ th}{R_{S}}}} & (3)\end{matrix}$

FIG. 4 is a simplified diagram showing a power conversion systemaccording to another embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The system 400 includes a system controller 402, resistors 408, 409, 418and 467, a full-wave rectifying bridge 413, capacitors 424, 434 and 442,a inductor 420, a diode 422, and LEDs 498. The system controller 402includes switches 430 and 432, diodes 436 and 450, a resistor 436, avoltage clamper 452, a reference signal generator 458, an input-voltagedetector 460, an enable controller 462, a demagnetization detector 464,a valley detector 466, a control logic component 468, a comparator 470,a driving component 472, a summation component 474, ahigh-low-input-line-voltage-compensation component 476, and a leadingedge blanking (LEB) component 478. In addition, the system controller202 includes terminals 431, 440, 446, 448 and 454. For example, theswitch 430 includes a transistor (e.g., a field effect transistor, aninsulated-gate bipolar transistor, or a bipolar junction transistor). Inanother example, the switch 432 includes a transistor (e.g., a fieldeffect transistor, an insulated-gate bipolar transistor or a bipolarjunction transistor).

In some embodiments, the resistors 408, 409, 416 and 467, the full-waverectifying bridge 413, the capacitors 424, 434 and 442, the inductor420, and the diode 422 are the same a the resistors 208, 209, 216 and267, the full-wave rectifying bridge 213, the capacitors 224, 234 and242, the inductor 220, and the diode 222, respectively. In certainembodiments, the switches 430 and 432, the diodes 438 and 450, theresistor 436, the voltage clamper 452, the reference signal generator458, the input-voltage detector 460, the enable controller 462, thedemagnetization detector 464, the valley detector 466, the control logiccomponent 468, the comparator 470, the driving component 472, thesummation component 474, the high-low-input-line-voltage-compensationcomponent 476, and the LEB component 478 are the same as the switches230 and 232, the diodes 238 and 250, the resistor 236, the voltageclamper 252, the reference signal generator 258, the input-voltagedetector 260, the enable controller 262, the demagnetization detector264, the valley detector 266, the control logic component 268, thecomparator 270, the driving component 272, the summation component 274,the high-low-input-line-voltage-compensation component 276, and the LEBcomponent 278, respectively. In some embodiments, the system 400performs similar operations as the system 200.

FIG. 5 is a simplified diagram showing a power conversion systemaccording to yet another embodiment of the present invention. Thisdiagram is merely a example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The system 1400 includes a system controller 1402, resistors 1418 and1467, a full-wave rectifying bridge 1413, capacitors 1424, 1434 and1442, an inductor 1420, a diode 1422, and LEDs 1498. The systemcontroller 1402 includes switches 1430 and 1432, diodes 1438 end 1450, avoltage clamper 1452, a reference signal generator 1458, a timingcomparison component 1460, an over-voltage-protection (OVP) component1462, a demagnetization detector 1464, a maximum-on-time component 1465,a valley detector 1466, a control logic component 1468, a comparator1470, a driving component 1472, a summation component 1474, ahigh-low-input-line-voltage-compensation component 1476, and a LEBcomponent 1478. In addition, the system controller 1402 includesterminals 1431, 1440, 1446 and 1448. For example, the switch 1430includes a transistor (e.g., a field effect transistor, aninsulated-gate bipolar transistor, or a bipolar junction transistor). Inanother example, the switch 1432 includes a transistor (e.g., a fieldeffect transistor, an insulated-gate bipolar transistor or a bipolarjunction transistor). In another example, the terminal 1448 (e.g.,terminal GND) is biased at a ground voltage 1404 (e.g., chip ground). Inyet another example, the resistor 1436 and the diode 1438 are configuredto adjust a turn-on/turn-off speed of the switch 1430. As n example, avoltage associated with agate terminal of the switch 1430 is notconstant when the switch 1430 is turned on or turned off. As anotherexample, the voltage associated with the gate terminal of the switch1430 is approximately constant long before or after the switch 1430 isturned on or turned oft.

According to one embodiment, a AC input 1410 (e.g., VAC) is provided toinput terminals 1412 and 1414, and the rectifying bridge 1413 isconfigured, together with the capacitor 1442, to provide a voltage 1401(e.g., V_(bus)). For example, the control logic component 1468 outputs amodulation signal 1482 (e.g., a pulse-width-modulation signal) to thedriving component 1472 that generates a drive signal 1483 to affect theswitch 1432. In another example, the switch 1432 and the switch 1430 weconnected in cascode. In yet another example, the switch 1432 is closedor opened for power switching. In yet another example, during an on-timeperiod of the switch 1432, the switch 1432 is closed (e.g., being turnedon). In yet another example, a signal 1484 associated with a node (e.g.,node SW) between the switches 1430 and 1432 decreases in magnitude, andin response the switch 1430 is closed (e.g., being turned on). In yetmother example, the inductor 1420 is magnetized, and a current 1490flows through the switch 1430 and is received by the system controller1402 at the terminal 1431. In yet another example, a voltage 1437associated with a node between the switch 1430 and the inductor 1420decreases in magnitude. In yet another example, a voltage signal 1406associated with the resistor 1467 is detected by the system controller1402 at the terminal 1446 (e.g., terminal CS), and the LEB component1478 receives the signal 1406 and outputs a current sensing signal 1477to the comparator 1470. In yet another example, during an off-timeperiod of a switching cycle associated with the drive signal 1483, theswitch 1432 is open (e.g., being turned off). In yet another example,the signal 1484 increases in magnitude, and in response the switch 1430is opened (e.g., being turned off). In yet another example, the inductor1420 is demagnetized, and a current 1492 flows through the inductor1420. As an example, the current 1492 flows through the diode 1422 andis provided to the capacitor 1424 and the LEDs 1498. In yet anotherexample, the signal 1437 increases in magnitude (e.g., to become closeto the voltage 1401). In yet another example, an output current 1488that flows through the LEDs 1498 is associated with (e.g., equal to) anaverage current flowing through the inductor 1420. In yet anotherexample, if the average current flowing through the inductor 1420 isregulated to a predetermined magnitude, the output current 1488 thatflows through the LEDs 1498 is regulated to be approximately constant ata predetermined magnitude.

According to another embodiment, the signal 1484 associated with thenode SW between the switches 1430 and 1432 is received by thedemagnetization detector 1464 that is configured to determine ademagnetization period associated with the inductor 1420. For example,the valley detector 1466 receives a detection signal 1485 from thedemagnetization detector 1464 and outputs a signal 1486 to the controllogic component 1468. As an example, the valley detector 1466 detects afirst valley appearing in the signal 1484 and changes the signal 1486 sothat a rising edge appears in the drive signal 1483 and an on-timeperiod of a switching cycle associated with the drive signal 1483begins. For example, the output current 1488 is estimated based on atleast information associated with the signal 1406 and thedemagnetization period associated with the inductor 1420.

According to yet another embodiment, during a start-up process of thesystem 1400, the capacitor 1434 is charged in response to the voltagesignal 1401 (e.g., through the resistor 1418), and a voltage 1435increases in magnitude. For example, if the voltage 1435 becomes largerthan a start-up threshold voltage, the controller 1402 begins tooperate. In another example, when the switch 1432 is opened (e.g., beingturned oft), the voltage signal 1437 begins to increase in magnitudeimmediately after the switch 1432 is opened. As an example, the switch1430, the inductor 1420 and the associated parasitic capacitances beginto oscillate. In another example, one or more spikes begin to appear inthe signal 1484 associated with the node (e.g., node SW) between theswitch 1430 and the switch 1432. In yet another example, if the one ormore spikes are larger than a clamping voltage associated with thevoltage clamper 1452 (e.g., a zener diode) plus a forward voltageassociated with the diode 1450, the spikes are absorbed by the capacitor1434 and the voltage clamper 1452 through the diode 1450. In yet anotherexample, the one or more spikes provide supply charges or currents tothe capacitor 1434 to provide a supply voltage to the controller 1402through the terminal 1440 (e.g., terminal VCC). In yet another example,all internal circuits of the controller 1402 obtain power through theterminal 1440 (e.g., terminal VCC). In yet another example, thesummation component 1474 receives a compensation signal 1471 from thehigh-low-input-line-voltage-compensation component 1476 and a referencesignal 1473 and outputs a threshold signal 1475 to the comparator 1470that outputs a comparison signal 1499. In yet another example, if theinput line voltage (e.g., the signal 1401) has a large magnitude, thesignal 1471 has a small magnitude (e.g., 0). In yet another example, ifthe input line voltage (e.g., the signal 1401) has a small magnitude,the signal 1471 has a large magnitude. In yet another example, if thecomparison signal 1499 changes from a first logic level (e.g., 1) to asecond logic level (e.g., 0) which indicates that the current sensingsignal 1477 becomes larger than the threshold signal 1475 in magnitude,the drive signal 1483 decreases in magnitude (e.g., from a logic high toa logic low) and an on-time period of a switching cycle associated withthe drive signal 1483 ends.

According to yet another embodiment, the timing comparison component1460 receives the detection signal 1485 and outputs a signal 1480 to theOVP component 1462. For example, the OVP component 1462 also receivesthe comparison signal 1499 and the modulation signal 1482 and generatesa signal 1481 to the control logic component 1468. In another example,the demagnetization period is inversely proportional to an outputvoltage associated with the LEDs 1498, as follows:

$\begin{matrix}{V_{out} = \frac{{IL\_ P} \times L}{T_{demag}}} & (4)\end{matrix}$

where V_(out) represents the output voltage associated with the LEDs1498, IL_P represents a peak magnitude of the current 1492, L representsan inductance of the inductor 1420 and T_(demag) represents a durationof the demagnetization period. According to Equation 4, if the peakmagnitude of the current 1492 keeps approximately constant, the higherthe output voltage (e.g., increasing in magnitude), the shorter thedemagnetization periods (e.g., decreasing in magnitude), in someembodiments.

In one embodiment, the timing comparison component 1460 compares thedemagnetization period with a predetermined time period which startsfrom a beginning of the demagnetization process associated with theinductor 1420. For example, if, during a switch cycle, the comparisonsignal 1499 indicates that the current sensing signal 1477 is largerthan or equal to the threshold signal 1475 in magnitude, and if, duringan off-time period of the switch cycle, the demagnetization period issmaller than the predetermined time period, the over-voltage protectionis triggered. As an example, the signal 1480 changes to indicate thatthe demagnetization period is smaller than the predetermined timeperiod, and in response the OVP component 1482 changes the signal 1481to shut down the system 1400. As another example, the OVP component 1482changes the signal 1481 from a first signal state (e.g., correspondingto a first logic level) to a second signal state (e.g., corresponding toa second logic level) to shut down the system 1400. In another example,during and after the shut-down process, the signal 1483 is equal to aground voltage in magnitude, so that the switch 1432 (e.g., M1) is open(e.g., being turned off) for a long period of time.

In another embodiment, the AC input 1410 is not applied (e.g., beingturned off). For example, the supply voltage provided through theterminal 1440 (e.g., terminal VCC) decreases in magnitude to becomesmaller than a first predetermined threshold (e.g., a under-voltagelock-up threshold), and in response, the internal circuits of thecontroller 1402 are reset to certain initial conditions. In yet anotherembodiment, after the internal circuits of the controller 1402 have beenreset to the certain initial conditions, the AC input 1410 is applied(e.g., being tuned on) again. For example, the supply voltage providedthrough the terminal 1440 (e.g., terminal VCC) increases in magnitude tobecome larger than a second predetermined threshold (e.g., apower-on-reset threshold), and in response, the controller 1402 beginsnormal operations again.

In yet another embodiment, if, during an on-time period of a switchcycle related to the switch 1432, the comparison signal 1499 indicatesthat the current sensing signal 1477 keeps being smaller than thethreshold signal 1475 in magnitude, the OVP component 1462 does notchange the signal 1481 and the signal 1481 would not case the system1400 to stop outputting signals (e.g., the over-voltage protection notbeing triggered) so that the switch 1432 is kept open (e.g., being tunedoft) for a long time period, regardless of whether the signal 1480indicates that the demagnetization period is smaller than thepredetermined time period. For example, if the current sensing signal1477 is larger than the threshold signal 1475 in magnitude, thecomparison signal 1499 is at a logic low level. In another example, oncethe OVP component 1482 changes the signal 1481 to shut down the system1400, the OVP component 1482 no longer changes the signal 1481 inresponse to the signal 1480, the signal 1499 and/or the signal 1482. Inyet another example, the maximum-on-time component 1465 detects abeginning of a on-time period of a switching cycle associated with thedrive signal 1483 based on at least information associated with thesignal 1486 and determines whether the on-time period exceeds a maximumon-time period. If the on-time period exceeds the maximum on-timeperiod, the maximum-on-time component 1465 outputs a signal 1455 to thecontrol logic component 1468 to change the drive signal 1483 to open(e.g., turn oil) the switch 1432.

In yet another embodiment, during a on-time period of each switch cycleassociated with the switch 1432, if the signal 1499 does not indicatethat the current sensing signal 1477 is larger than or equal to thethreshold signal 1475 in magnitude, the OVP component 1462 is in anabnormal operation mode. For example, the OVP component 1462 does notrespond to the output of the timing comparison component 1460 (e.g.,associated with the comparison result of the demagnetization period andthe predetermined time period). As an example, the OVP operations areprohibited and the on-time period of the switch 1432 corresponds to amaximum on-time period. But if the signal 1499 indicates that thecurrent sensing signal 1477 is larger than or equal to the thresholdsignal 1475 in magnitude, the OVP component 1462 responds to the outputof the timing comparison component 1460, and the OVP operations areenabled, according to certain embodiments. For example, the OVPcomponent 1462 enters the normal operation mode and remains in thenormal operation mode. In another example, if the current sensing signal1477 is larger than or equal to the threshold signal 1475 in magnitude,the modulation signal 1482 is changed to indicate that the on-timeperiod of the switch cycle has ended and an off-time period begins. Inyet another example, during the off-time period of the switch cycle, theswitch 1432 is open (e.g., being tuned oil).

In yet another embodiment, when the demagnetization process ends, thevalley detector 1466 outputs the signal 1486 to change the modulationsignal 1482 to indicate that an off-time period of the switch cycle hasended, the next switch cycle starts. For example, during a on-timeperiod of the next switch cycle, if the signal 1499 does not indicatethat the current sensing signal 1477 is larger than or equal to thethreshold signal 1475 in magnitude, the OVP component 1462 is in theabnormal operation mode. As an example, the OVP component 1462 does notrespond to the output of the timing comparison component 1460 (e.g.,associated with the comparison result of the demagnetization period andthe predetermined time period). As an example, the OVP operations areprohibited and the on-time period of the switch 1432 corresponds to amaximum on-time period. But if the signal 1499 indicates that thecurrent sensing signal 1477 is larger than or equal to the thresholdsignal 1475 in magnitude, the OVP component 1462 responds to the outputof the timing comparison component 1460, and the OVP operations areenabled, according to certain embodiments. For example, the OVPcomponent 1462 enters the normal operation mode and remains in thenormal operation mode. In another example, if the current sensing signal1477 is larger then or equal to the threshold signal 1475 in magnitude,the modulation signal 1482 is changed to indicate that the on-timeperiod of the switch cycle has ended and an off-time period begins.

According to one embodiment, if the OVP component 1462 is in theabnormal operation mode, the OVP component 1462 keeps the signal 1481 ata particular logic level (e.g., a logic low, 0) regardless of thesignals 1480 so that the signal 1481 would not cause the system 1400 tobe shut down due to mistakenly triggered over-voltage protection. Forexample, if the OVP component 1462 is in the normal operation mode andthe demagnetization period is no smaller than the predetermined timeperiod, in response to the signal 1480 indicating that thedemagnetization period is no smaller than the predetermined time period,the signal 1481 remains unchanged and does not cause the system 1400 tobe shut down.

According to another embodiment, if the OVP component 1462 is in thenormal operation mode and the demagnetization period is smaller then thepredetermined time period, in response to the signal 1480 indicates thatthe demagnetization period is smaller then the predetermined timeperiod, the OVP component 1482 changes the signal 1481 in order to shutdown the system 1400. For example, after the OVP component 1482 changesthe signal 1481 to shut down the system 1400, the signal 1481 willremain the same regardless of the signal 1480, the signal 1499, end/or1482.

FIG. 6 is a simplified diagram showing a power conversion systemaccording to yet another embodiment of the present invention. Thisdiagram is merely n example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The system 500 includes a system controller 502, resistors 508, 509,518, 536 and 567, a full-wave rectifying bridge 513, capacitors 524, 534and 342, a switch 530, an inductor 520, diodes 522 and 538, and LEDs596. The system controller 502 includes a switch 532, a diode 550, avoltage clamper 552, a reference signal generator 558, a input-voltagedetector 560, enable controller 562, a demagnetization detector 564, avalley detector 566, a control logic component 568, a comparator 570, adriving component 572, an error amplifier 574, a compensation-networkcomponent 576, a sampling component 561 and a LEB component 578. Inaddition, the system controller 502 includes terminals 531, 540, 546,548 and 554. For example, the switch 530 includes a transistor (e.g., afield effect transistor, a insulated-gate bipolar transistor, or abipolar junction transistor). In another example, the switch 532includes a transistor (e.g., a field effect transistor, aninsulated-gate bipolar transistor or a bipolar junction transistor).

According to one embodiment, the resistors 508, 509, 518, 536 and 567,the full-wave rectifying bridge 513, the capacitors 524, 534 and 542,the switch 530, the inductor 520, and the diodes 522 and 538 are thesame as the resistors 208, 209, 218, 236 and 267, the full-waverectifying bridge 213, the capacitors 224, 234 and 242, the switch 230,the inductor 220, and the diodes 222 and 238, respectively. For example,the switch 532, the diode 550, the voltage clamper 552, the referencesignal generator 558, the input-voltage detector 560, the enablecontroller 562, the demagnetization detector 564, the valley detector566, the control logic component 568, the driving component 572, and theLEB component 578 are the same as the switch 232, the diode 250, thevoltage clamper 252, the reference signal generator 258, theinput-voltage detector 260, the enable controller 262, thedemagnetization detector 264, the valley detector 266, the control logiccomponent 268, the driving component 272, and the LEB component 278,respectively.

According to one embodiment, an AC input 510 (e.g., VAC) is provided toinput terminals 512 and 514, and the rectifying bridge 513 isconfigured, together with the capacitor 542, to provide a voltage 501(e.g., V_(bus)). For example, the voltage 501 (e.g., V_(bus)) isprocessed by a voltage divider including the resistors 508 and 509, andthe system controller 502 receives an input signal 519 at the terminal554 (e.g., terminal V_(in)). In another example, the input-voltagedetector 560 receives the input signal 519 and outputs a signal 580 tothe enable controller 562 that generates a signal 581 to the controllogic component 568. In yet another example, the control logic component568 outputs a modulation signal 582 to the driving component 572 thatgenerates a drive signal 583 to affect the switch 532.

According to another embodiment, the switch 532 and the switch 530 areconnected in cascode. For example, the switch 532 is closed or openedfor power switching. In another example, during an on-time period of theswitch 532, the switch 532 is closed (e.g., being turned on). In yetanother example, a signal 584 associated with a node (e.g., node SW)between the switches 530 and 532 decreases in magnitude, end in responsethe switch 530 is closed (e.g., being turned on). In yet anotherexample, the inductor 520 is magnetized, and a current 590 flows throughthe switch 530 and is received by the system controller 502 at theterminal 531. In yet another example, a voltage 537 associated with anode between the switch 530 and the inductor 520 decreases in magnitude.In yet another example, a voltage signal 506 associated with theresistor 367 is detected by the system controller 502 at the terminal546 (e.g., terminal CS), and the LEB component 578 receives the signal506 and outputs a current sensing signal 577 to the comparator 570. Inyet another example, during an off-time period of a switching cycleassociated with the drive signal 583, the switch 532 is open (e.g.,being tuned off). In yet another example, the signal 584 increases inmagnitude, and in response the switch 530 is opened (e.g., being turnedoff). In yet another example, the inductor 520 is demagnetized, and acurrent 592 flows through the diode 522, the capacitor 524, and the LEDs598. In yet another example, the signal 537 increases in magnitude(e.g., to become close to the voltage 501). In yet another example, theerror amplifier 574 includes a transconductance amplifier. In yetanother example, the error amplifier 574 is implemented as part of anintegrator.

According to yet another embodiment, an output current 588 that flowsthrough the LEDs 598 is associated with (e.g., equal to) an averagecurrent flowing through the inductor 520. For example, if the system 500operates in a quasi-resonant (QR) mode, the average current flowingthrough the inductor 520 is approximately equal to half of a peakmagnitude of the current 590. In another example, one or more peakmagnitudes of the current sensing signal 577 during one or more previousswitching periods associated the switch 532 are detected (e.g., sampled)by the sampling component 561 that outputs a signal 551. In yet anotherexample, the error amplifier 574 receives the signal 551 and a referencesignal 553 and amplifies a difference between the signal 551 and thereference signal 553. In yet another example, the error amplifier 574outputs a signal 555 (e.g., a current signal) to thecompensation-network component 576 that outputs a signal 557 to thecomparator 570. In yet another example, the comparator 570 compares thesignal 557 and the current sensing signal 577 and outputs a comparisonsignal 559 to the control logic component 568 so as to affect one ormore peak magnitudes of the current 590 during one or more nextswitching periods associated with the switch 532 so that the averagecurrent flowing through the inductor 520 is regulated. In yet anotherexample, if the comparison signal 559 changes from a first logic level(e.g., 1) to a second logic level (e.g., 0) which indicates that thecurrent sensing signal 577 becomes larger than the signal 557 inmagnitude, the drive signal 583 changes from the first logic level(e.g., 1) to the second logic level (e.g., 0) and an on-time period of aswitching cycle associated with the drive signal 583 ends. In yetanother example, the first logic level corresponds to 5 volts, and thesecond logic level corresponds to 0 volt.

According to yet another embodiment, the signal 584 associated with thenode SW between the switches 530 and 532 is received by thedemagnetization detector 564 that is configured to determine ademagnetization period associated with the inductor 520. For example,the valley detector 566 receives a detection signal 585 from thedemagnetization detector 564 and outputs a signal 586 to the controllogic component 568. As an example, the valley detector 566 detects afirst valley appearing in the signal 584, and changes the signal 586 sothat the drive signal 583 changes from the second logic level (e.g., 0)to the first logic level (e.g., 1) and an on-time period of a switchingcycle associated with the drive signal 583 begins. For example, themagnitude of the output current 588 can be estimated based on at leastinformation associated with the signal 506 and the demagnetizationperiod associated with the inductor 520.

In one embodiment, during a start-up process of the system 500, thecapacitor 534 is charged in response to the voltage signal 501 (e.g.,through the resistor 518), and a voltage 535 increases in magnitude. Forexample, if the voltage 535 becomes larger than a start-up thresholdvoltage, the controller 502 begins to operate. As an example, the signal519 related to (e.g., proportional to) the voltage signal 501 is sensedby the input-voltage detector 560. As another example, if the voltagesignal 501 is larger than a predetermined threshold, the enablecontroller 562 outputs the signal 581 (e.g., at a logic high level). Asyet another example, the control logic component 568 outputs themodulation signal 582 to tur an and off the switch 532 at a modulationfrequency so that the system 200 operates normally and the LEDs 298 areturned on. As yet another example, if the voltage signal 501 is smallerthan the predetermined threshold, the controller 502 is in an off mode,and the enable controller 562 outputs the signal 581 (e.g., at a logiclow level) so that the control logic component 568 does not output themodulation signal 582 to turn on and off the switch 532 at themodulation frequency. As yet another example, the switch 532 keeps beingopen (e.g., being turned off), so that there is little current flowingthrough the LEDs 598 which is not turned on. In some embodiments, thevoltage signal 501 is always sensed by the input-voltage detector 560during the operation of the system 500. In other embodiments, thevoltage signal 501 is sensed by the input-voltage detector 560 duringthe start-up process and/or a short time period thereafter. In someembodiments, during the start-up process, once the voltage signal 501becomes larger than the predetermined threshold, the enable controller562 outputs the signal 581 so that the system 500 starts operation. Forexample, once the system 500 starts operation, even if the signal 501becomes smaller than the predetermined threshold, the enable controller562 does not change the signal 581 and the signal 581 remains at a samelogic level (e.g., the logic low level), so that the system 500continues normal operations.

In another embodiment, when the switch 532 is opened (e.g., being turnedoff), the voltage 537 begins to increase in magnitude immediately afterthe switch 532 is opened. For example, the switch 530, the inductor 520and the associated parasitic capacitances begin to oscillate. In anotherexample, one or more spikes begin to appear in the signal 584 associatedwith the node (e.g., node SW) between the switch 530 and the switch 532.In yet another example, if the one or more spikes are larger than aclamping voltage associated with the voltage clamper 552 (e.g., a zenerdiode) plus a forward voltage associated with the diode 550, the spikesare absorbed by the capacitor 534 and the voltage clamper 552 throughthe diode 550. In yet another example, the one or more spikes providesupply charges or currents to the capacitor 534 to provide a supplyvoltage to the controller 502 through the terminal 540 (e.g., terminalVCC). In yet another example, all internal circuits of the controller502 obtain power through the terminal 540 (e.g., terminal VCC).

FIG. 7 is a simplified diagram showing a power conversion systemaccording to yet another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The system 600 includes a system controller 602, resistors 608, 609,618, and 667, a full-wave rectifying bridge 613, capacitors 624, 634 and642, an inductor 620, a diode 622, and LEDs 698. The system controller602 includes a switch 632, diodes 638 and 650, a resistor 636, a voltageclamper 652, a reference signal generator 658, a input-voltage detector660, a enable controller 662, a demagnetization detector 664, a valleydetector 666, a control logic component 668, a comparator 670, a drivingcomponent 672, error amplifier 674, a compensation-network component676, a sampling component 661 and a LEB component 678. In addition, thesystem controller 602 includes terminals 631, 640, 646, 648 and 654. Forexample, the switch 630 includes a transistor (e.g., a field effecttransistor, un insulated-gate bipolar transistor, or a bipolar junctiontransistor). In another example, the switch 632 includes a transistor(e.g., a field effect transistor, an insulated-gate bipolar transistoror a bipolar junction transistor).

According to one embodiment, the resistors 606, 609, 618, 636 and 667,the full-wave rectifying bridge 613, the capacitors 624, 634 and 642,the switch 630, the inductor 620, and the diodes 622 and 638 are thesame as the resistors 508, 509, 518, 536 and 567, the full-waverectifying bridge 513, the capacitors 524, 534, and 542, the switch 530,the inductor 520, and the diodes 522 and 538, respectively. For example,the switch 632, the diode 650, the voltage clamper 652, the referencesignal generator 658, the input-voltage detector 660, the enablecontroller 662, the demagnetization detector 664, the valley detector666, the control logic component 668, the driving component 672, thecomparator 670, the error amplifier 674, the compensation-networkcomponent 676, the sampling component 661, and the LEB component 678 arethe same as the switch 532, the diode 550, the voltage clamper 552, thereference signal generator 558, the input-voltage detector 560, theenable controller 562, the demagnetization detector 564, the valleydetector 566, the control logic component 568, the driving component572, the comparator 570, the error amplifier 574, thecompensation-network component 576, the sampling component 561, and theLEB component 578, respectively. In some embodiments, the system 600performs similar operations as the system 500.

FIG. 8 is a simplified timing diagram for demagnetization detection ofthe power conversion system 200 as shown in FIG. 2 , the powerconversion system 400 as shown in FIG. 4 , the power conversion system500 as shown in FIG. 6 and/or the power conversion system 600 as shownin FIG. 7 according to some embodiments of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in de art would recognize manyvariations, alternatives, and modifications.

For example, the waveforms 702, 704 and 706 describe certain operationsof the power conversion system 200 that operates in a discontinuousconduction mode (DCM), certain operations of the power conversion system400 that operates in a discontinuous conduction mode (DCM), certainoperations of the power conversion system 500 that operates in adiscontinuous conduction mode (DCM), and/or certain operations of thepower conversion system 600 that operates in a discontinuous conductionmode (DCM). In another example, the waveform 702 represents the signal237 as a function of time, the waveform 704 represents the signal 284 asa function of time, and the waveform 706 represents a slope of thesignal 284 as a function of time. In yet another example, an on-timeperiod, T_(on), starts at time t₅ and ends at time t₆, and ademagnetization period, T_(demag), starts at the time t₆ and ends attime t₇. In yet another example, t₅≤t₆≤t₇.

According to one embodiment, during the on-time period (e.g., T_(on)),both the switch 230 and the switch 232 are closed (e.g., being turnedon). For example, the current 290 that flows through the switch 230increases in magnitude. In another example, the signal 237 (e.g., V_(D))and the signal 284 (e.g., V_(SW)) have low magnitudes (e.g., as shown bythe waveform 702 and the waveform 704 respectively). In yet anotherexample, if both the switch 230 and the switch 232 are open (e.g., beingturned off), the current 290 reduces to a low magnitude (e.g., zero),and the demagnetization process starts. For example, during thedemagnetization period T_(demag), the signal 237 (e.g., V_(D)) isapproximately at a magnitude 708 (e.g., as shown by the waveform 702),and the signal 284 (e.g., V_(SW)) is approximately at a magnitude 710(e.g., as shown by the waveform 704). In yet another example, thedemagnetization process ends at the time t₇. For example, the signal 284(e.g., V_(SW)) decreases rapidly in magnitude (e.g., as shown by thewaveform 704). In another example, the demagnetization can be detectedbased on information associated with the signal 284 (e.g., V_(SW)).

As discussed above and further emphasized here, FIG. 8 is merelyexamples, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, though the above discussion of FIG. 8 isbased on the timing diagram of the power conversion system 200 operatingin the DCM mode, the scheme for demagnetization detection applies to thepower conversion system 200 operating in the continuous conduction modeor in the quasi-resonant mode according to certain embodiments. As anexample, the waveform 702 represents a signal 437 associated with a nodebetween the switch 430 and the inductor 420 as a function of time thewaveform 704 represents a signal 484 associated with a node between theswitch 430 and the switch 432 as a function of time, and the waveform706 represents a slope of the signal 484 as a function of time. Inanother example, the waveform 702 represents the signal 537 as afunction of time, the waveform 704 represents the signal 584 as afunction of time, and the waveform 706 represents a slope of the signal584 as a function of time. As another example, the waveform 702represents a signal 637 associated with a node between the switch 630end the inductor 620 as a function of time, the waveform 704 representsa signal 684 associated with a node between the switch 630 and theswitch 632 as a function of time, and the waveform 706 represents aslope of the signal 684 as a function of time.

FIG. 9 is a simplified diagram showing certain components of thedemagnetization detector 264 as part of the power conversion system 200as shown in FIG. 2 , certain components of the demagnetization detector464 as part of the power conversion system 400 as shown in FIG. 4 ,certain components of the demagnetization detector 564 as part of thepower conversion system 500 as shown in FIG. 6 , and/or certaincomponents of the demagnetization detector 664 as part of the powerconversion system 600 as shown in FIG. 7 according to some embodimentsof the present invention. This diagram is merely an example, whichshould not unduly limit the scope of the claims. One of ordinary skillin the art would recognize many variations, alternatives, andmodifications. For example, the demagnetization detector 264 includes acapacitor 802, two resistors 804 and 806, a comparator 808, a blankingcomponent 810, a timing control component 812, two flip-flop components814 and 819, a NOT gate 816, and an AND gate 818.

According to one embodiment, the signal 284 (e.g., V_(SW)) is receivedat the capacitor 802. For example, the slope of the signal 284 isdetected using a differentiator including the capacitor 802 and theresistors 804 and 806. In another example, a differentiated signal 820is generated, and is equal to the slope of the signal 284 plus adirect-current (DC) offset V_(m). In yet another example, the DC offsetV_(m) is determined based on the following equation.

$\begin{matrix}{V_{m} = {V_{{ref}1} \times \frac{R_{4}}{R_{3} + R_{4}}}} & (5)\end{matrix}$

where V_(m) represents the DC offset, V_(ref1) represents a referencevoltage 824, R₃ represents the resistance of the resistor 804, and R₄represents the resistance of the resistor 806.

According to another embodiment, the comparator 808 receives thedifferentiated signal 820 and a threshold signal 822 and outputs acomparison signal 826 to the blanking component 810 to affect theflip-flop components 814 and 816. For example, the drive signal 283 isreceived by the blanking component 810 and the timing control component812 to affect the flip-flop components 814 and 816. In another example,for each switching cycle, a demagnetization process starts when theswitch 232 is open (e.g., off) in response to the drive signal 283. Inyet another example, during the demagnetization process, thedifferentiated signal 820 is no less than the threshold signal 822 inmagnitude. In yet another example, if the differentiated signal 820becomes smaller than the threshold signal 822 in magnitude, then the endof the demagnetization process is detected. In yet another example, thecomparator 808 changes the comparison signal 826 in order to change thedetection signal 285.

As discussed above and further emphasized here, FIG. 9 is merelyexamples, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternativesand modifications. For example, though the above discussion of FIG. 9 isbased on the diagram of the demagnetization detector 264 as part of thepower conversion system 200, the scheme for demagnetization detectionapplies to the demagnetization detector 464 as part of the powerconversion system 400, the demagnetization detector 564 as part of thepower conversion system 500, and/or the demagnetization detector 664 aspart of the power conversion system 600.

According to one embodiment, a system controller for regulating a powerconversion system includes: a detection component configured to receivean input voltage related to a diode connected to an inductor and outputa first signal at a first logic level in response to the input voltagebeing larger than a predetermined threshold; a control logic componentconfigured to receive the first signal, process information associatedwith the first signal, and output a modulation signal related to amodulation frequency in response to the first signal being at the firstlogic level; and a driving component configured to receive themodulation signal and output a drive signal to open ad close a firstswitch at the modulation frequency, so that in response to the firstswitch being closed, the inductor is configured to output a firstcurrent through the switch and in response to the first switch beingopen, the inductor is configured to output a second current through thediode. For example, the system controller is implemented according to atleast FIG. 2 . FIG. 4 , FIG. 5 , FIG. 6 , and/or FIG. 7 .

According to another embodiment, a system controller for regulating apower conversion system includes: a first transistor including a firsttransistor terminal, a second transistor terminal, and a thirdtransistor terminal, the first transistor terminal being coupled to afourth transistor terminal of a second transistor, the second transistorfurther including a fifth transistor terminal and a sixth transistorterminal. The fifth transistor terminal is coupled to a first resistorterminal of a first resistor, the first resistor further including asecond resistor terminal. The fifth transistor terminal is coupled to afirst diode terminal of a first diode, the first diode further includinga second diode terminal. The second diode terminal is coupled to thesecond resistor terminal. The system controller is configured to changea first voltage of the fourth transistor terminal to turn on and off thesecond transistor and to affect a current flowing through a inductor.For example, the system controller is implemented according to at leastFIG. 2 , FIG. 4 , FIG. 5 , FIG. 6 , and/or FIG. 7 .

According to yet another embodiment, a system controller for regulatinga power conversion system includes: a sampling component configured todetect one or more peak magnitudes of a current sensing signalassociated with a first current from an inductor flowing through aswitch and generate an output signal based on at least informationassociated with the detected one or more peak magnitudes of the currentsensing signal; a error amplifier configured to receive the outputsignal and a reference signal and generate an amplified signal based onat least information associated with the output signal and the referencesignal; a comparator configured to receive the current sensing signaland a first signal associated with the amplified signal and output acomparison signal based on at least information associated with thefirst signal and the current sensing signal; and a control-and-drivecomponent configured to receive the comparison signal and output a drivesignal based on at least information associated with the comparisonsignal to close or open the switch to affect the first current. Forexample, the system controller is implemented according to at least FIG.2 , FIG. 4 , FIG. 5 , FIG. 6 , and/or FIG. 7 .

According to yet another embodiment, a system controller for regulatinga power conversion system includes: a protection component configured toreceive a first signal and a second signal and generate a third signalbased on at least information associated with the first signal and thesecond signal, the first signal being associated with a demagnetizationperiod related to an inductor, the second signal being associated with afirst current flowing through the inductor; and a control-and-drivecomponent configured to receive the third signal and output a drivesignal to the switch to affect the first current. The protectioncomponent is further configured to, in response to, the second signalindicating, during a first switching cycle associated with the drivesignal, that the first current is equal to or larger than a currentthreshold, and the first signal indicating, during an off-time period ofthe first switching cycle, that the demagnetization period is smallerthan a predetermined time period, change the third signal from a firstsignal state to a second signal state to cause the power conversionsystem to be shut down. For example, the system controller isimplemented according to at least FIG. 5 .

In one embodiment, a method for regulating a power conversion systemincludes: receiving am input voltage related to a diode connected to aninductor; processing information associated with the input signal;outputting a first signal at a first logic level in response to theinput voltage being larger than a predetermined threshold; receiving thefirst signal; and processing information associated with the firstsignal. The method further includes: outputting a modulation signalrelated to a modulation frequency in response to the first signal beingat the first logic level; receiving the modulation signal; andprocessing information associated with the modulation signal. Inaddition, the method includes: outputting a drive signal to open andclose a first switch at the modulation frequency; in response to thefirst switch being closed, outputting a first current through theswitch; aid in response to the first switch being open, outputting asecond current through the diode. For example, the method is implementedaccording to at lot FIG. 2 , FIG. 4 , FIG. 5 , FIG. 6 , and/or FIG. 7 .

In another embodiment, a method for regulating a power conversion systemincludes: sampling one or more peak magnitudes of a current sensingsignal associated with a first current from an inductor flowing througha switch; generating an output signal based on at lot informationassociated with the detected one or more peak magnitudes of the currentsensing signal; receiving the output signal and a reference signal; andprocessing information associated with the output signal and thereference signal. The method further includes: generating an amplifiedsignal based on at least information associated with the output signaland the reference signal; receiving the current sensing signal and afirst signal associated with the amplified signal; processinginformation associated with the current sensing signal and the firstsignal; and outputting a comparison signal based on at least informationassociated with the first signal and the current sensing signal.Furthermore, the method includes: receiving the comparison signal;processing information associated with the comparison signal; andoutputting a drive signal based on at least information associated withthe comparison signal to close or open the switch to affect the firstcurrent. For example, the method is implemented according to at leastFIG. 2 , FIG. 4 , FIG. 3 . FIG. 6 , and/or FIG. 7 .

In yet another embodiment, a method for regulating a power conversionsystem includes: receiving a first signal and a second signal;processing information associated with the first signal and the secondsignal; and generating a third signal based on at least informationassociated with the first signal and the second signal, the first signalbeing associated with a demagnetization period related to an inductor,the second signal being associated with a first current flowing throughthe inductor. The method further includes: receiving the third signal;processing information associated with the third signal; outputting adrive signal to the switch to affect the first current; and in responseto, the second signal indicating, during a first switching cycleassociated with the drive signal, that the first current is equal to orlarger than a current threshold and the first signal indicating, duringan off-time period of the first switching cycle, that thedemagnetization period is smaller than a predetermined time period,changing the third signal from a first signal state to a second signalstate to cause the power conversion system to be shut down. For example,the method is implemented according to at least FIG. 5 .

For example, some or all components of various embodiments of thepresent invention each are individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

1.-29. (canceled)
 30. A system controller for regulating a powerconversion system, the system controller comprising: a first transistorincluding a first transistor terminal, a second transistor terminal, anda third transistor terminal, the first transistor terminal being coupledto a fourth transistor terminal of a second transistor, the secondtransistor further including a fifth transistor terminal and a sixthtransistor terminal; wherein: the fifth transistor terminal is coupledto a first resistor terminal of a first resistor, the first resistorfurther including a second resistor terminal; the fifth transistorterminal is coupled to a first diode terminal of a first diode, thefirst diode further including a second diode terminal; the second diodeterminal is coupled to the second resistor terminal; wherein the systemcontroller is configured to turn on and off the second transistor. 31.The system controller of claim 30 is further configured to keep a secondvoltage of the fifth transistor terminal constant and change a firstvoltage of the fourth transistor terminal to turn on and off the secondtransistor.
 32. The system controller of claim 30, further comprising: afirst controller terminal coupled to the second resistor terminal andthe second diode terminal; and a second diode including a third diodeterminal and a fourth diode terminal, the third diode terminal beingcoupled to the first controller terminal, the fourth diode terminalbeing coupled to the first transistor terminal.
 33. The systemcontroller of claim 32, further comprising: a clamping componentconfigured to keep a second voltage associated with the first controllerterminal from exceeding a predetermined threshold.
 34. The systemcontroller of claim 32 wherein the first controller terminal is coupledto a capacitor including a first capacitor terminal and a secondcapacitor terminal.
 35. The system controller of claim 32 wherein thefirst capacitor terminal is coupled to the second resistor terminal andthe second diode terminal.
 36. A system controller for regulating apower conversion system, the system controller comprising: a protectorconfigured to receive a first signal and a second signal and generate athird signal based on at least information associated with the firstsignal and the second signal, the first signal being associated with ademagnetization period related to a inductor; and a driver configured toreceive the third signal and output a drive signal; wherein: theprotector is further configured to, in response to, the second signalindicating, during a first switching cycle associated with the drivesignal, that the first current is equal to or larger than a currentthreshold, and the first signal indicating, during an off-time period ofthe first switching cycle, that the demagnetization period is smallerthan a predetermined time period, change the third signal from a firstsignal state to a second signal state to cause the power conversionsystem to be shut down.
 37. The system controller of claim 36 whereinthe controller is further configured to, in response to the third signalbeing at the first signal state, output the drive signal to lone or opena switch.
 38. The system controller of claim 36, further comprising: acomparator configured to receive a current sensing signal associatedwith the first current and a threshold signal associated with thecurrent threshold and generate the second signal based on at leastinformation associated with the current sensing signal and the thresholdsignal.
 39. The system controller of claim 36, further comprising: amaximum-on-time component configured to determine whether an on-timeperiod of a second switching cycle associated with the drive signalexceeds a maximum on-time period and generate a fourth signal based anat let information associated with the on-time period; wherein thecontroller is further configured to, in response to the fourth signalindicating the on-time period exceeds the maximum on-time period, endthe on-time period of the second switching cycle and change the drivesignal to open a switch.
 40. The system controller of claim 36, whereinthe controller includes: a control-logic component configured to receivethe protection signal and generate a modulation signal; and a drivingcomponent configured to receive the modulation signal and output thedrive signal based on at let information associated with the modulationsignal.
 41. The system controller of claim 40 wherein the protector isfurther configured to receive the modulation signal and detect a end ofthe off-time period of the first switching cycle.
 42. A method forregulating a power conversion system, the method comprising receiving afirst signal and a second signal; processing information associated withthe first signal and the second signal; generating a third signal basedon at least information associated with the first signal and the secondsignal, the first signal being associated with a demagnetization periodrelated to a inductor; receiving the third signal; processinginformation associated with the third signal; outputting a drive signal;and in response to, the second signal indicating, during a firstswitching cycle associated with the drive signal, that the first currentis equal to or larger the a current threshold and the first signalindicating, during an off-time period of the first switching cycle, thatthe demagnetization period is smeller then a predetermined time period,changing the third signal from a first signal state to a second signalstate to cause the power conversion system to be shut down.